X-ray films can be scanned by a film digitizer, and converted into digital format. Digitized films can then be stored for future retrieval or analyzed with image analysis algorithms such as Computer Aided Detection (CAD). Film digitizers are available from, for example, Canon, Howtek, Kodak, or Vidar. The film digitizer is, connected to a standard computer and a standard user interface controls scanning, identifying, and storing the digitized films as images on disk. Standard user interfaces for digitizer control, including quality control, error detection, and error recovery, are available from Vidar, Applicare, or Merge.
In the diagnosis process, quick and reliable identification of the film is required to increase the efficiency of the process and reduce the risk of errors associated with misidentification. Furthermore digitized X-ray films are often analyzed with software applications such as CAD and reliable association of the CAD results with the corresponding digitized X-ray film is very important.
In a typical scenario, the radiologist normally reads the film mammograms on an alternator or on a light box. Suspicious findings are noted by the radiologist, and recorded in a medical report. However, a non-zero percentage of cancers are typically missed by radiologists. To decrease the rate of false negative, a second radiologist may read the films, and the results of both radiologists are compared.
The results of CAD can be used in much the same way as a second radiologist. In one scenario, also referred to as “second read with CAD”, the radiologist first reads the films without the aid of a computer. Once the radiologist has noted her findings, she reviews the suspicious areas identified by CAD analysis, for example on a monitor as an overlay over the digitized versions of the mammogram, or printed on paper. The suspicious areas may confirm the findings of the radiologist. Or, the radiologist may be prompted to re-examine areas she had not found to be suspicious, but which were highlighted by the computer.
In another scenario, also referred as “cued read with CAD”, the radiologist may read the films and review the CAD results at the same time, moving back and forth between them using the CAD results to “cue” her reading.
In either scenario, it is important to ensure that the CAD results are properly associated with the X-ray films to ensure correct identification of the results and avoid “mix-up” of the films and CAD results. Commercial products currently use a number of methods for to achieve this.
For example a bar code system can be used. When films are digitized, a separator sheet of the same approximate size of the films is also scanned. It serves as a separator between the films of one case and the films of the next case. A bar code is printed on the separator sheet. The digitization system reads the bar code, and digitally associates it with the images. The operator enters no patient name, accession number, or other identifier, the bar code information is the identifier of the case only the numerical identifier corresponding to the bar code (a number) identifies the patient. After the digitization, the films are replaced in the jacket, together with the separator sheet with the bar code.
When the films are hung on the alternator, a bar code reader is used to scan the bar code on separator sheets. The alternator contains a computer and logic to associate the CAD results with a particular alternator position (that of the corresponding X-ray films). That way, the proper digital images and CAD results are displayed on the mini-monitors integrated into the alternator depending on the alternator position. The numerical identifier corresponding to the bar code (together with the alternator position) identities the patient.
This method is deficient in that radiologists and other medical personnel use patient names and patient record identifiers to identify patients, and cross-correlate patients to other medical information, reports, requisitions, and the like. Since the CAD results are identified only with a barcode and its associated numerical identifier, association of patient names or records with CAD results involves an indirect and unreliable cross-referencing method from CAD results to bar code to patient name. This method is not only inconvenient and time consuming, but also prone to errors.
In other systems a bar code sticker is affixed to each individual film (the sticker includes the orientation information of each individual film). The digitizer uses the bar code to associate it with the films of the patient. When the films are reviewed, a bar code reader is used to read the bar code stickers on the films, and the appropriate images are displayed on a monitor, together with the CAD results. In this system the CAD results are not associated with alternator positions. This method is equally deficient in that the only mechanism to correlate CAD results with a patient name is to cross-correlate the bar code numbers of the CAD results with a bar code label affixed to an X-ray film.
Yet another method is, described in “Hybrid display for simultaneous side-by-side review of radiographs”, U.S. Pat. No. 5,748,173. In the described system, patient information in the form of a name or a patient number is obtained directly from the film that is placed on a view box (alternator or light box) using a bar code scanner or a CCD camera. This method is also deficient in that the CAD results have to be identified by other means with the patient name or patient number before they can be recalled with the method described here.
Other strategies have also been used to identify X-ray films. For example the operator can enter the patient name and identification. The patient name is then digitally associated with the digitized images. When a case is reviewed, the radiologist enters the patient name in a computer, and the appropriate images and CAD results are displayed. Alternatively, the radiologist can select the patient name from a list. A disadvantage of this method is that the patient name has to be entered manually at the time of digitization, and potentially again at the time of review.